Surveillance techniques have been greatly improved with the advent of modern electro-optic technology. Miniature Charge Coupled Device (CCD) cameras and transmitters have made daytime surveillance possible from locations previously unavailable. By way of example, highly sensitive CCD arrays with micro-lenses have extended the nighttime surveillance capability out to near-starlight conditions. With an image intensifier (sometimes denoted herein as I 2) coupled to a CCD array, remote surveillance by starlight is a reality. The prior art has miniaturized the CCD and I 2 combination to a form compatible with nearly all practical applications requiring compactness. However, the CCD and I 2 combination also requires some small quantity of visible light in order to function. As the available source light diminishes--such as during overcast, nighttime conditions--the imagery gets spotty and unusable.
Infrared (IR) imagers extend surveillance beyond starlight into no-light conditions. Visible light is not required for IR imaging because the self-emission of objects in the infrared suffices for their operation. In the infrared, the scenery at nighttime appears the same as the scenery in the daytime. This feature brings the added benefit that camouflaged targets are revealed by self-luminance. For example, men hiding in undergrowth emit due to the heat of their bodies and are easily revealed in the IR image.
The prior art IR cameras are large and unwieldy as compared to the CCD and I 2 combination discussed above. By way of example, one of the first practical IR cameras was a mechanically scanned Forward Looking Infrared (FLIR) system that is bulky, fragile, power intensive, and that requires cryogenic cooling to reduce detector noise. The FLIR system has been improved with the two-dimensional IR focal plane array (FPA), which does not require a mechanical scanner and which is therefore sturdier and less unwieldy than the FLIR. However, the IR FPA still requires cryogenic cooling. This cooling makes it impractical to construct lightweight and compact IR systems, such as that required for unmanned reconnaissance vehicles.
One development in infrared technology concerns "uncooled" IR focal plane arrays. The uncooled FPA is nearly analogous to the CCD array: it is small, sturdy, requires no cooling, and is made from common silicon materials. The uncooled camera permits viewing of IR scenes without the use of coolers and is, therefore, useful in applications requiring compactness. Two of the common uncooled FPAs include: microbolometers, which are essentially miniaturized versions of the common bolometer detector (see, e.g., The Infrared Handbook edited by Wolfe et al., Office for Naval Research, 11-20 (1978); and ferroelectric devices, which measure temperature differences by sensing polarization-induced charge differentials, see, Id., 11-58.
Lockheed-Martin IR Imaging Systems (formerly Loral Infrared and Imaging Systems) makes one prior art uncooled microbolometer FPA. The Lockheed-Martin FPA measures approximately 2".times.2".times.1/2", and the associated electronics board measures about 2".times.3".times.1/2". There is an integrated circuit imbedded within a silicon substrate adjacent to each microbolometer which permits selective processing of the thermal signals.
Texas Instruments makes a competing ferroelectric uncooled FPA. It too has similar size and permits the acquisition of IR imagery without the use of cryogenic coolers and mechanical scanners.
The uncooled FPAs of the prior art have useful application in many areas of thermal imaging. However, their use in miniaturized IR cameras, and in particular within IR cameras designated for unmanned vehicles, is problematic. First, the interface between the sensor and the electronics is unwieldy when configured within the confines of an unmanned vehicle. Second, the optical designs which focus the IR radiation onto the detectors are generally large and impractical for miniaturized applications. Third, the uncooled cameras of the prior art typically require choppers to provide for thermal and/or noise calibration of the FPA. These choppers, again, add cost, weight, and limit compactness. Fourth, certain prior art uncooled FPAs and associated electronics are "tuned" to each other. Accordingly, FPAs and their electronics are not generally modular such that either can be removed and replaced efficiently.
It is, accordingly, an object of the invention to provide a compact IR camera that overcomes most, if not all, of the above-referenced problems.
Another object of the invention is to provide methodology for manufacturing miniaturized IR cameras and unmanned reconnaissance vehicles.
Still another object of the invention is to provide compact optical designs for application with IR cameras and remotely piloted vehicles.
Still another object of the invention includes methodology for calibrating IR cameras in unmanned vehicles without use of moving shutters or choppers.
One other object of the invention provides for tying electronic boards to IR FPAs in a reconfigurable manner to facilitate mounting within housings of selectable shape while maintaining a single production line.
Yet another object of the invention is to provide a compact, IR reconnaissance vehicle.
And another object of the invention is to provide a modular, miniaturized IR FPA and electronics capable of mating and demating with other such IR FPAs and electronics, without complex calibration or tuning.
These and other objects will become apparent in the description which follows.